Yesterday, fellow blogger Steve Sande hopped into the TUAW backchannel all fussed. As part of some iMovie troubleshooting he was doing with Apple's support wizards, he was trying to get his new iMac to boot into the recovery partition and was getting nowhere. Holding down the Option key during reboot wasn't showing the volume as an option the way he expected.
Has this happened to you? Well, there's a reason the recovery partition didn't show up -- Steve was working with a Fusion drive-based system.
We started by checking that the disk contained the recovery partition. To do this, I had Steve launch the Terminal app and enter "diskutil list" (no quotes) at the command line. As you can see in the screenshot above, there was a "Recovery HD" partition listed under /dev/disk1.
After confirming the partition, I recommended that Steve use the standard Command-R trick. You press and hold Command-R during reboot to choose the recovery partition. (Using Command-Option-R starts Internet Recovery for completely hosed systems where you need to to install a new drive.)
A few quick Google searches later, we realized that Fusion drives seem to disallow the option-key-then-select-Recovery-volume-to-boot-from trick so many of us are used to. Apparently, this applies to both Apple-shipped Fusion drives as well as roll-your-own solutions.
Fusion Drives also use a unique version of Disk Utility. As this Apple knowledge base article points out, "The version of Disk Utility that comes with Fusion Drive is unique. Earlier versions of Disk Utility can't be used with a Fusion Drive."